The experiments proposed herein are designed to yield an accurate and relatively detailed picture of the immune response to SV40 TSTA during the course of primary SV40 virus-induced tumorigenesis, with particular emphasis on the balance among those factors - cell-mediated immunity, homoral immunity and free, circulating tumor-associated antigen (TSTA) - which are thought to govern the ultimate fate of the tumor in the host. The methods used will be the tumor cell neutralization and transplantation rejection tests in vivo and the macrophage migration inhibition and microcytoxicity assays in vitro. The results obtained with these techniques have all be shown to correlate with one another. Immunologic parameters which may govern the resistance or susceptibility to SV40-induced neoplasia will also be investigated. Finally, immunotherapeutic protocols will be studied for their ultimate effects on the fate of the tumor in the host. This final outcome of tumor development will be correlated with the cell-mediated immune response of the host to SV40 TSTA after immunization, as well as with the levels of free antigen and/or circulating blocking factors elicited in the host. The system in which these experiments will be conducted bears a very close resemblance to that model presently thought to represent the events leading to human neoplasia. The results obtained in this model tumor system may therefore have great potential for clinical applicability in the design of immunotherapeutic protocols for the successful treatment and/or prevention of human cancer.